Putting a child to bed is an important part of the day for a parent as well as for the child. It is important for the child to get a good night of sleep, and it is important for the parent to know that the child is safely in bed. One of the issues with putting a child in bed is making sure that they will stay in bed and sleep, and not try to get up and move around the house. This is an age-old problem with children who are either not tired, or want to stay awake for some other reason. Many potential issues can arise if a child is out of bed without knowledge of the parent or caretaker.
Often it is preferable to monitor other persons' sleep habits, such as the elderly, the ill, or persons affected by sleepwalking or other sleep disorders as many of the same issues presented by children at bed time can affect other persons as well.
There are solutions available in the market for detecting when people of all ages are out of bed, but these can be prone to false alarms, e.g. if a child stirs, it may send a warning to a parent that the child is out of bed. Many of the present solutions are systems created specifically for elderly patients in hospital or assisted-living type settings. These types of solutions can render false readings because they may not be properly calibrated for the more aggressive movements of a child. Additionally, many of the solutions are integrated into a hospital-type bed, which can be cost prohibitive.
A Force Sensing Resistor (FSR) can be less expensive than other force measuring devices, such as a force cell or piezoelectric devices. However, an FSR cannot provide an accurate measure of force, such as a precision scale. These devices are typically used in applications such as a button, where force is applied momentarily and then fully released, the resistance change can be very large and the two states (press/release) can be easily determined. When used with a constant load, there are issues that can arise that need correction if a robust indication in change of force is to be enjoyed. Additionally, the FSR can exhibit other disadvantages, such that it can have poor repeatability even with a momentary addition/removal of the same weight; it can vary its value with temperature; it can drift significantly—usually the resistance can drift down under constant load over time, especially if there is a constant load on the FSR—such as the weight of an empty bed—or constant load of bed plus an occupant. This drift can be accentuated when the sensor is placed on a carpet, especially at first as the sensor sinks into the carpet.
Thus, a key issue to be overcome when monitoring children is the relative weight of the child to the bed that needs to be differentiated by the bed check device circuitry when there is a small change in resistance in the FSR, unlike a button press as given in an earlier example. Comparatively, it is also much easier to see a large change in weight of an adult relative to the existing weight of a bed. Typical values for a bed sensors for children are as follows: The bed can weigh ˜12-26 pounds; Average toddler boys can weigh 17.5 to 38 pounds; Average toddler girls can weigh 19 to 38 pounds. The relatively small difference between the weight of the bed leg and the weight of a child can be challenging to discern, especially combined with the drift and other issues cited above with FSR technology. To overcome this, the FSR needs to be continuously calibrated.
Another potential issue is the removal of noise and other errant readings. Since the detection circuitry needs to be able to detect a smaller range of weight differences, as with children, it need to thus be more sensitive. However this sensitivity can create issues such as false readings caused by, for example, the floor shaking as people are walking or running in the house, a clothes washer or dryer shaking the floor under the sensor, or a wiggly child in the bed, crawling across the bed, or jumping up and down in the bed, causing false alarms.
Accordingly, there is a need for a device that can enjoy the benefits of using an FSR to monitor a child's presence in the bed, while overcoming its disadvantages. What is needed is a cost effective, reliable solution that can accurately alert a caretaker to let them know if and when a child or other person has left their bed.